The enhancement of the lesion after injection of contrast material will also be quantitatively analyzed by use of a time-signal intensity curve analysis software package that can display the signal intensity-versus-time curve in the region of interest during the process of enhancement. A region of interest with the size and shape fitted to the lesion will be drawn manually and positioned at the lesion. Another region of interest of the same size and shape will be positioned in the lumen of the carotid artery. The carotid lesion and lumen signal intensity-versus-time curves will be produced. The degree of enhancement of the lesion during constant flow of the contrast material (steady-state) will be measured by looking at the enhanced intensity in the plaque and the ratio of the enhanced intensity (dB) in the lesion to that in the lumen of the artery.